IPSec to TP-Link down after 2.3.1p5

[julianbros]

Hello all!

After upgrading my PfSense from 2.1.4 to the latest available version I'm running into an error.
Site A is my PfSense Firewall with public IP.
Site B is my TP-Link TL-R600VPN behind my Cable Router and I configured static local IP on the TP-Links WAN interface.
(10.10.254.251).

Ports 500 and 4500 are redirected from the cable router directly to this IP of the TP-Link.

TP-Link and PfSense were working together till the update. I've chosen aggressive mode with SHA-1, AES-256, DH2 and Lifetime 28800 for Phase 1, DPD enabled.
Phase 2 is nearly the same, but lifetime is 3600.

I've read about some IPSec errors in 2.3.X.
However Site C (Pfsense 2.3.1) is working finde.

Any suggestions?